Lung cancer develops through genetic and epigenetic abnormalities to key regulators of cell proliferation, differentiation, and apoptosis. Heterogeneit of these aberrations among patients contributes to the minimal efficacy of lung cancer treatments and has prompted a renewed focus on personalized therapy. Epigenetic therapy can simultaneously target hundreds of genes aberrantly silenced by methylation; however, the number and type of methylated genes within a tumor could influence its effectiveness. Recent studies show significant correlation between clinical response to epigenetic therapy and demethylation of candidate genes. Our own findings revealed that a combination therapy with inhibitors of DNA methyltransferases (5-Aza) and histone deacetylase (MS-275) profoundly affected the growth of orthotopic human lung tumors by primarily targeting poorly differentiated cells and inducing demethylation of polycomb repressive complex (PRC2) target genes. Based on these findings we hypothesized that three factors could impact the response of lung cancer patients to epigenetic therapy: the level of differentiation, total number of methylated genes, and the number of PRC2 target genes silenced within a tumor. The major barrier limiting the discovery of such prognostic biomarkers in clinical samples is the very limited access to pre- and post-therapy tumors. In this study we circumvent this limitation by treating lung cancer patients with one cycle of 5-Aza and MS-275 combination prior to tumor resection. Therapeutic efficacy will be evaluated through comparison of genome-wide changes in methylation and gene expression between matched pre- and post-therapy tumors. The utility of discovered biomarkers to predict clinical responses will be evaluated through collaboration with ongoing Stand-up-to- Cancer (SU2C) clinical trials that are using continuous cycles of the same 5-Aza and MS-275 regimens in metastatic lung cancer patients. Furthermore, the recent National Lung Screening Trial (NLST) revealed that the use of CT-scan for lung cancer screening significantly increased early detection and reduced lung cancer mortality by 20.0% over chest radiology. However, despite the use of this most advanced technology lung cancer mortality remains high, underlining the fact that improved therapy is also urgently needed for early stage lung cancer. Even with curative intent surgery, 40% of early stage patients die from recurrent disease within 5 years of resection. As a result postoperative adjuvant therapy is now recommended for some lung cancer patients. A recent groundbreaking discovery demonstrated that tumor-associated methylation in histologically tumor-free lymph nodes (LN) can identify early recurring patients that could benefit from adjuvant therapy. Our studies will advance these exciting discoveries further by exploring the impact of adjuvant epigenetic therapy on the incidence and timing of tumor recurrence in patients with methylation positive or negative LN. Thus, results from the proposed studies will make significant contributions to the improvement of lung cancer therapy and advance the current understanding about the disease and its management.